ReDex: An Android Bytecode Optimizer

ReDex is an Android bytecode (dex) optimizer originally developed at Facebook. It provides a framework for reading, writing, and analyzing .dex files, and a set of optimization passes that use this framework to improve the bytecode. An APK optimized by ReDex should be smaller and faster than its source.

Quick Start Guide

Dependencies

We use package managers to resolve third-party library dependencies.

Mac OS X

You will need Xcode with command line tools installed. To get the command line tools, use:

xcode-select --install 

Install dependencies using homebrew:

brew install autoconf automake libtool python3 brew install boost jsoncpp 

Ubuntu 14.04 LTS (64-bit)

sudo apt-get install \
  g++ \
  automake \
  autoconf \
  autoconf-archive \
  libtool \
  libboost-all-dev \
  liblz4-dev \
  liblzma-dev \
  make \
  zlib1g-dev \
  binutils-dev \
  libjemalloc-dev \
  libiberty-dev \
  libjsoncpp-dev 

Experimental: Windows 10 (64-bit)

You need Visual Studio 2017. Visual Studio 2015 is also possible, but a couple of C++ compile errors need to be fixed. We use vcpkg for dependencies. Install vcpkg from their document:

cd c:\tools git clone https://github.com/Microsoft/vcpkg.git cd vcpkg .\bootstrap-vcpkg.bat .\vcpkg integrate install 

Install necessary libraries with x64-windows-static:

.\vcpkg install boost --triplet x64-windows-static .\vcpkg install zlib --triplet x64-windows-static .\vcpkg install jsoncpp --triplet x64-windows-static 

Download, Build and Install

Get ReDex from GitHub:

git clone https://github.com/facebook/redex.git cd redex 

Now, build ReDex using autoconf and make.

# if you're using gcc, please use gcc-4.9 autoreconf -ivf && ./configure && make -j4 sudo make install 

Experimental: CMake for Mac, Linux, and Windows

Alternatively, build using CMake. Note that the current CMakeLists.txt only implements a rule for redex-all binary. We will support installation and testing soon.

Generate build files. By default, it uses Makefile:

# Assume you are in redex directory mkdir build-cmake cd build-cmake # .. is the root source directory of Redex cmake .. 

If you prefer the ninja build system:

cmake .. -G Ninja 

On Windows, first, get CMAKE_TOOLCHAIN_FILE from the output of "vcpkg integrate install", and then:

cmake .. -G "Visual Studio 15 2017 Win64"`  -DVCPKG_TARGET_TRIPLET=x64-windows-static`  -DCMAKE_TOOLCHAIN_FILE="C:/tools/vcpkg/scripts/buildsystems/vcpkg.cmake" 

Build redex-all:

cmake --build . 

On Windows, you may build from Visual Studio. Redex.sln has been generated.

You should see a redex-all executable, and the executable should show about 45 passes.

./redex-all --show-passes 

Test

Optionally, you can run our unit test suite. We use gtest, which is downloaded via a setup script.

./test/setup.sh cd test make check 

Usage

To use ReDex, first build your app and find the APK for it. Then run:

redex path/to/your.apk -o path/to/output.apk 

If you want some statistics about each pass, you can turn on tracing:

export TRACE=1 

The result output.apk should be smaller and faster than the input. Enjoy!

Documentation

Right now we have a limited amount of documentation which describes a few example Redex optimization passes as well as deployments of Redex (including Docker).

More Information

The blog Optimizing Android bytecode with ReDex provides an overview of the Redex project.

Issues

Issues on GitHub are assigned priorities which reflect their urgency and how soon they are likely to be addressed.

• P0: Unbreak now! A serious issue which should have someone working on it right now.
• P1: High Priority. An important issue that someone should be actively working on.
• P2: Mid Priority. An important issue which is in the queue to be processed soon.
• P3: Low Priority. An important issue which may get dealt with at a later date.
• P4: Wishlist: An issue with merit but low priority which is up for grabs but likely to be pruned if not addressed after a reasonable period.

License

ReDex is BSD-licensed. We also provide an additional patent grant.

FAQ

I'm getting "Couldn't find zipalign. See README.md to resolve this"

zipalign is an optimization step that is bundled with the Android SDK. You need to tell redex where to find it. For example, if you installed the SDK at /path/to/android/sdk, try:

ANDROID_SDK=/path/to/android/sdk redex [... arguments ...] 

You can alternatively add zipalign to your PATH, for example:

PATH=/path/to/android/sdk/build-tools/xx.y.zz:$PATH redex [... arguments ...] 

My app fails to install with Failure [INSTALL_PARSE_FAILED_NO_CERTIFICATES]

After you run redex, you'll need to re-sign your app. You can re-sign manually using these instructions: http://developer.android.com/tools/publishing/app-signing.html#signing-manually.

You can also tell redex to sign for you. If you want to sign with the debug key, you can simply do:

redex --sign [ ... arguments ...] 

If you want to sign with your release key, you'll need to provide the appropriate args:

--sign Sign the apk after optimizing it -s [KEYSTORE], --keystore [KEYSTORE] -a [KEYALIAS], --keyalias [KEYALIAS] -p [KEYPASS], --keypass [KEYPASS] 

My App crashes with MethodNotFoundException, ClassNotFoundException, NoSuchFieldException, or something similar. How do I fix this?

Redex probably deleted or renamed it. Redex is quite aggressive about deleting things it deems are unreachable. But, often Redex doesn't know about reflection or other complex ways an entity could be reached.

Here's how you ensure Redex will not delete or rename something:

Annotate any class, method, or field you want to keep with @DoNotStrip.

Add this to your redex config (at the uppermost level of the json) to prevent deletion:

"keep_annotations": [
"Lcom/path/to/your/DoNotStrip;" ] 

and add this to your config to prevent renaming:

"RenameClassesPassV2" : {

"dont_rename_annotated": [
  "Lcom/path/to/your/DoNotStrip;"
] 
}
 

and define DoNotStrip:

package com.path.to.your; public @interface DoNotStrip {

}
 

How does this compare to ProGuard?

ReDex is conceptually similar to ProGuard, in that both optimize bytecode. ReDex, however, optimizes .dex bytecode, while ProGuard optimizes .class bytecode before it is lowered to .dex. Operating on .dex is sometimes an advantage: you can consider the number of virtual registers used by a method that is an inlining candidate, and you can control the layout of classes within a dex file. But ProGuard has many capabilities that ReDex does not (for example, ReDex will not remove unused method parameters, which ProGuard does).

In our opinion, comparing ReDex and ProGuard is a bit apples-and-oranges, since we have focused on optimizations that add value on top of ProGuard. We use both tools to optimize the Facebook app. Our reported performance and size improvements (about 25% on both dex size and cold start time) are based on using ReDex on an app already optimized with ProGuard. We have no plans to measure performance without ProGuard.

How about DexGuard?

DexGuard operates on dex, but we haven't evaluated it at all since it's closed source. We don't use it at Facebook and we have no plans to start.